Galvanized steel utilized in the automotive, construction and appliance industries is formed in very thin strips (0.015 to 0.060 inch thick), which are passed through a molten bath of either zinc (galvanizing), aluminum (aluminizing), or aluminum/zinc (galvanneal, galfan, galvalume, etc.), in which the levels of aluminum vary from a fraction of a percent to as much as 100 percent.
The "hot dip" metalizing coating process requires equipment that runs submerged in the molten metal. The molten metal temperature usually varies from as low as 820.degree. F. to as high as 1300.degree. F.
A heated metal pot contains a bath of molten zinc/aluminum. A continuous moving strip of low carbon steel is introduced into the bath from a furnace in the conventional manner. The strip passes around a sink roll and tensor rolls while submerged in the bath, so the surface of the strip picks up a zinc/aluminum coating. The strip is delivered to the bath through a conventional tubular snout. The interior of the snout housing contains an inert gas such as nitrogen or a mix of nitrogen and hydrogen. This procedure, as is well known to those skilled in the art, is useful in preventing the steel strip from oxidizing.
Because of the extremely large dimensions of the equipment and in spite of efforts to prevent all possible air leaks into the furnace, small leaks do occur, generating ferrous oxides (Fe.sub.2 O.sub.3.FeO, etc.) When the steel strip enters the bath, a chemical process occurs in which the melt in the bath reacts with the iron in the steel strip (inducing the coating) but also reacts with the oxides to form dross that contains ZnFe, ZnAlFe, ZnFe+Al.sub.2 O.sub.3, etc. The free iron settles to the bottom of the molten metal pot. Because of the slightly or nearly identical density to the molten metal, the oxides (Al.sub.2 O.sub.3, ZnO) and the intermetallics formed (ZnFe, ZnAlFe, etc.) remain in suspension or float to the surface in the form of dross. The dross increases its concentration by being nearly entrapped in the zone comprised by the snout, the strip, the sink roll and the tensor rolls, where it gradually forms deposits on top of the sink roll and the strip being processed.